Optical sensors, such as optical proximity sensors, may include one or more light emitting elements (e.g., LEDs) and an adjacent photosensitive light detector, where the sensor can estimate proximity of an object based on the magnitude of reflected light from the one or more LEDs returning to the sensor. The value of these sensors has become more important in the recent past with the advent of battery-operated handheld devices, such as mobile phones. For example, a fair amount of the energy from a mobile phone battery is used to drive the display, and there is value in turning off the display or backlight when the mobile phone or other device is brought to the user's ear (where it cannot be viewed anyway). Optical proximity sensors have been used for this, and many other applications.
For other examples, there are many other applications in which the presence of an object can be detected with an optical proximity sensor to advantage. These range from sensing when protective covers have been opened on machinery, paper has been positioned correctly in a printer, or an operator's hands are at risk near an operating machine. An optical proximity sensor can also be used as a simple touch or near-touch activated switch, and could be implemented in applications like keyboards or devices that have a plastic housing that is sealed but which allows the light from the source to pass through and be sensed by the detector on the return.
Light from the source to the detector that does not project out of the package to the target, but rather is transmitted directly from the source to the detector, reduces the capability of the overall device to sense distance. Such light essentially propagates sideways within the package and is considered noise or “light leakage”, and contains no information. To reduce and preferably prevent light leakage, a light barrier is often used to isolate the light source from the light detector. However, current techniques for manufacturing optical proximity sensors are relatively complex, costly and often results in sensors that are larger than desired. Further, the optical proximity sensor components except the light source are often produced by one vendor, while the light source is produced by another vendor, resulting in the light source being installed separately from the rest of the components of the optical proximity sensor, which increases the overall footprint of the device, and the complexity and the cost of the assembly.
Optical sensors are often used with (e.g., placed behind or covered by) a cover plate that is glass, plastic, or some other protective light transmissive material. For example, the cover plate can be the glass covering a screen of a mobile phone, portable music player or personal data assistant (PDA), or the plastic covering a screen of a laptop computer. When such a cover plate is placed over an optical sensor, the optical sensor is often susceptible to specular reflections. Just as it is desirable to minimize light being transmitted directly from the source to the detector, it is also desirable to minimize the specular reflections because such reflections similarly reduce the capability of the overall device to sense distance, since specular reflections are essentially noise that contain no information.